JACKSONVILLE, Fla. – Many of us woke up to another freeze and frost Wednesday morning. The coldest spots generally were west of the metro where some areas reported temperatures in the 20s and 30s.
What exactly is frost, and how does it form?
Let’s say, for example, the dew point is in the low 30s. Dew point is a measure of the amount of moisture in the air. During the day, the sun heats up our planet and in this scenario, temperatures have warmed into the low 60s. Frost clearly can’t form with temperatures well above freezing!
However, at night it’s a different story. Let’s say, for example, we have a very cold night on the way and temperatures are forecast to drop to the low 30s.
At night, heat rises and cools the surface. Cooling is in fact, faster under clearer skies due to more energy escaping the atmosphere. Cooling also forces moisture onto the ground. In this example, the temperature is 35 degrees, several degrees above the dew point.
However, when temperatures fall close to the dew point (pictured above), condensation occurs and moisture freezes allowing frost to form. Frost is a thin layer of ice crystals, which you can see below.
Joshua Miller
Very very cold morning.
You might have noticed that frost is visible on elevated and grassy surfaces.
Pavement is a darker color, which absorbs more sunlight, meaning it retains more heat. At night, pavement temperatures could be in the 40s, while grassy surfaces are much cooler. The pavement releases heat much more slowly compared to the non-pavement surface.
Therefore, road surfaces will take longer to reach freezing and grassy surfaces fall to freezing earlier, allowing frost to develop.
Another frost/freeze is possible Thursday night, especially north and west of the metro.